Firefighters and other personnel who must enter hazardous atmospheres are routinely provided with breathing apparatus. Such apparatus regularly includes some kind of mask or headgear which supplies the wearer with breathing air to the exclusion of the hazardous atmosphere.
This class of protective equipment is generally accepted, especially when it is used for breathing purposes during relatively brief periods of exertion. A firefighter who arrives at an incident, puts on the equipment, and works for a short time with it does endure a significant but still acceptable stress. Within a reasonably short period of time he will be out of the situation, either because it has been resolved, or because he must be relieved.
This degree of stress and exposure is respective to relatively routine events such as structural fires without involvement of severely toxic or poisonous gases, where the personnel can routinely approach the event, put on the apparatus, do the work, and then leave. In such events the stress is merely that of breathing filtered air, or of breathing air supplied from a tank. This is not necessarily a minor matter. Restrictions on breathing inherently tire a person, and this expenditure of energy reduces his capacity to perform the external services which called for his participation. However for many, even for most, organizations such as city fire departments in primarily residential cities, the existing situation is tolerable, and the equipment need be no more than tanks of breathing air and suitable face masks.
There are, however, more stringent situations, where the person must be clothed and on stand-by or be active for long periods of time and in which he must be nearly instantly able to exclude a hazardous atmosphere. Such situations can be found in firefighting where the generation of noxious gases is a risk but not yet an event, or in stand-by operations for ready crews such as for airport firefighters or participants in chemical warfare situations. For these men it is necessary to provide the greatest possible flexibility of breathing techniques, together with readily manipulable means to secure the man's safety and to select the most advantageous breathing mode for the moment. For example, he should be able to wear the full gear while being equipped in such a way that he can breathe ambient air, but on a moment's notice be able to change to a selected breathing mode to the exclusion of the ambient.
It is an object of this invention to provide breathing headgear which enables its wearer to be in various conditions of readiness, and quickly to select among various breathing modes, all for enabling him to remain ready or to be in action with least appropriate breathing stress at all times.